Antiskid device for car wheels especially for road vehicles

ABSTRACT

Anti-skid apparatus for vehicle wheels, particularly street vehicles, including a braking pressure control valve device which modulates the braking pressure as a function of specified values of a magnitude indicating the skid threshold of the wheels in response first, to release of braking pressure and subsequently to restoration of braking pressure, and throttle means with a movable throttle member for delaying the rate of build-up of braking pressure during the restoration phase.

United States Patent [1 1' Reinecke et al.

[ Nov. 20, 1973 ANTISKID DEVICE FOR CAR WHEELS ESPECIALLY FOR ROADVEHICLES 75 Inventors: Erich Reinecke,Beinhom; Fritz Assignee:

Filed:

Appl. No.:

Isernhagen, Letter; Alfred Klatt, Wettbergen; Erwin Holthusen, Itzehoe,all of Germany Westinghouse Bremsen-Uud Apparatebau GmbH, Hannover,Germany Jan. 17, 1972 Foreign Application Priority Data l l 27 3125 262e 303/21 CF, 21 LG [56] References Cited UNITED STATES PATENTS3,411,835 11/1968 Davis 188/181 A X Primary Examiner-Duane A. RegerAttorney-Ralph W. Mclntire, Jr.

[5 7 ABSTRACT Anti-skid apparatus for vehicle wheels, particularlystreet vehicles, including a braking pressure control valve device whichmodulates the braking pressure as a function of specified values of amagnitude indicating the skid threshold of the wheels in response first,to release of braking pressure and subsequently to restoration ofbraking pressure, and throttle means with a movable throttle member fordelaying the rate of build-up of braking pressure during the restorationphase.

11 Claims, 6 Drawing Figures till? 6 LF 6 PATENTEUHUYPO I975 mow New

. ANTISKID DEVICE FOR CAR WHEELS ESPECIALLY FOR ROAD VEHICLES BACKGROUNDOF THE INVENTION In some of the known anti-skid apparatus of the generalherein considered type, the throttle means is effective only in the laststage of restoration of braking pressure and remains effective untilbraking pressure has been completely restored. This type of apparatus isobjectionable in that the wheel is initially rapidly braked followingcomplete restoration of braking pressure, thereby hastening the tendencytoward a subsequent skid threshold without Obtaining maximum utilizationof the braking pressure.

In another known anti-skid apparatus of the general herein consideredtype, the throttle remains constantly in a throttling position so thatit is necessary to provide additional control means in order to supplyair pressure to the braking cylinder in bypassing relation to thethrottle means during normal rotation of the wheel.

In still another anti-skid device of the general herein considered type,the means for actuating the throttle means is very expensive from thestandpoint of construction and switching engineering.

SUMMARY OF THE INVENTION The inventionhas the purpose of providinganti-skid apparatus of the type mentioned above in which the throttle ischaracterized by simplicity of structure and which can be automaticallyrestored to an ineffective position when a specified, adjustable brakingpressure compatible with normal wheel" rotation is achieved. This taskis solved according to the invention in which the throttle meansincludes a throttle piston, which, in the throttling position, issubjected on one side to-pressure on the supply side of the throttleandon the otherside to pressure on the delivery side of the throttle,

such that the resultant force of pressure differential thus=establishedis directed against the forced a return spring by which thethrottlepiston canbe restoredfrom the throttling position to a non-throttlingposition when the force of the spring overcomes the opposing dissipatingdifferentialpressure force. In order: to improve the capacity of thewheel to utilize the braking force more efficiently at the end'of therestoration phase of braking pressure, the apparatus, according to theinvention, is provided with a return'spring of such compression ratingthat the force thereof overcomes the opposing differential forceofpressure acting onthe throttle piston beforethe restoration ofbraking'prese sure is completed. In order to simplify control of theinteraction of the throttle means with braking pressure within thebrakingpressure control valve device, an-.

other modification of the invention, is provided with a.

movable throttle member that ismoved by the braking pressure controlvalve mechanism into the throttling position'before the start of brakingpressure restoraionti-skidkapparatus according to one embodimentoftheinventionfincluding. throttle means incorporated: Y in a spool typebraking pressure control valve; device;

FIG. 2fshows a time-pressure diagram for'the antiskid apparatusaccording to. FIG. 1;

2 FIG. 3 shows a second embodiment of the anti-skid apparatus accordingto the invention including throttle means incorporated in a brakingpressure control valve DESCRIPTION AND OPERATION The anti-skid apparatusshown in FIG. 1 comprises a braking pressure spool type control valvedevice 1 which is interposed in a supply pipe line comprising pipes 4,5, and 6 leading from a source of fluid under pressurev or compressedair tank 2 to a single-acting braking cylinder device 3. A conventionaloperators brake valve device 7 is interposed between pipes 4 and 5, andtherefore is connected to the braking pressure control valve device 1,said brake valve device being selectively operable to a plurality ofpositions for effecting supply of fluid pressure from tank 2 at ameasured pressure commensurate with the selected position to which thebrake valve device is operated. The braking pressure control valvedevice 1 comprises a valve housing 8 provided with internally axiallyspaced annular" grooves 11', 1 2, 13 connectedby internal'coaxbetweengrooves 11 and 12 and between grooves 12 and 13, respectively. A spooltype valve assembly 14' comprises an annular vent valve 16, serving as avent valve member, axially fixed on a valve stem 17 extending coaxiallywithin housing 8, said vent valve being slidably and sealingly operablewithin land 10. A first operating piston 18 is coaxially fixed on theleft-hand end, as viewed in FIG. 1, a valve stem 17 and is operablyaffected by a magnetic valve device 19. Asecond operating piston 20 iscoaxially disposed in and adjacent the right-hand end of housing 8 andhas a pressure area greater than that of operating piston 18, and isprovided with a sleeve-like guide portion 21, into which the right-handend of stem 17 of the valve assembly 14 isslidably accommodated. Valveassembly 14 and operating piston 20 are axially movable relative to onean other and'have a spring 22 compressed therebetween with one endagainst'valve member 16 and the other end against piston 20, suchrelative movement being limited by abutment of portion 21 of piston 20against a shoulder'projection 23 formedon the adjacent side of valve 16.Operation of the piston 20 is effected by a magnet valve device 24;

An axially movable throttle assembly 15 comprisesa hollow throttlepiston 25 having a reduced diameter end portion, which cooperates withland 9to form 'a throttle area at '26. The throttle piston 25 is mountedcoaxially adjacent the left-hand end of valve stem 17 and is axiallymovable relative thereto. The left-hand end of throttle piston 25, asviewed in FIG. 1, moves with sliding sealing contact on a reduceddiamete'r'end 27 of stem 17, whereas the other end of said throttlepiston is slidably supported on an expanded diameter portion 28 of valvestem 17, which has a breather passage 29 formed thereon. A return spring30 is compressed within throttle piston 25 between portion 28 and theleft-hand end of said throttle piston. Relative movement betweenthrottle piston 25 and valve stem 17 is limited in a leftwardlydirection by operating piston 18 in the other or rightwardly directionby a shoulder formed on valve stem 17 adjacent expanded portion 28 andagainst which the throttle piston 25 may abut. The braking pressurecontrol valve device 1 controls communication between the tank 2 andbraking cylinder 3 via throttle area 26 in which land 9 acts as a valveseat, and the closing member is the throttle piston 25. An atmosphericcommunication for venting the braking cylinder 3 to atmosphere isestablished between pipe 6 and an atmospheric port 32 formed in valvehousing 8 when valve 16 is moved righwardly sufficiently to clear land10.

The magnetic valve devices 19 and 24 are actuated by a conventionalwheel-slip detector device 34 which is interposed in and closes or opensrespective energizing circuits 35 and 36 of the magnet valves when wheeldeceleration or acceleration of a certain value is attained by thewheel.

Operation of the anti-skid apparatus according to FIG. 1 is describedbelow with reference to the timepressure diagram as shown in FIG. 2.When the brakes are in a released state, the anti-skid apparatus is inthe disposition shown in FIG. 1, in which valve 16 of the brakingpressure control valve device 1 is closed, and throttle piston 25assumes an open or non-throttling position in which throttle area 26 isfully open so that throttling operation is inactive. If a brakeapplication is initiated by actuation of the operators brake valve 7,tank 2 is connected via pipes 4, 5, and 6, through control valve device1, to braking cylinder 3, and build-up of braking pressure up to apressure P,,, as represented by the curve P -P (FIG. 2), is initiated insaid braking cylinder Assuming that, when the effective braking pressureP (time point t,) is reached, the rotary deceleration rate of the wheelexceeds a value leading to skidding of the wheel, that is, at the skidthreshold thereof.

In response to a deceleration rate commensurate with the skid thresholdof the wheel, detector 34 is operated out of a normal position in whichenergizing circuits 35 and 36 of the respective magnet valve devices 19and 24 are open, to a first energizing position in which circuit 35 onlyis closed for causing magnet valve device 19 to operate a valve 37therein to an unseated or open position whereby operating piston 18 issubjected to fluid pressure from tank 2 via a pipe 38 and past saidunseated valve. Valve assembly 14 is moved rightwardly against spring 22out of a normal position, in which it is shown and was above whichthrottle area 26 is into a release position in a closed by throttlepiston 25 in a cut-off position and vent valve 16 open. During suchrightward movement of valve assembly 14, throttle piston 25 is carriedalong therewith by means of operating piston 18 which comes intoabutment therewith. As a result of this switching of the brakingpressure control valve 1, braking pressure in braking cylinder 3 isreduced in accordance with curve P P shown in FIG. 2, so that rotationof the wheel recovers sufficiently to cause the deceleration ratethereof to fall below the valve of skid threshold when a brakingpressure P (time point t,) is reached. in response to such rotationalrecovery of the wheel, detector device 34 is operated to a secondenergizing position in which energizing circuit 36 of magnetic valve 24is closed for causing said magnet valve device to operate a valve 39therein to an unseated or open position in which operating piston 20 issubjectedfvia a pipe 40 from tank 2, to the same pressure as that actingon operating piston 18. Guide portion 21 of operating piston 20 isbrought to rest against the shoulder proje t i ti'on' 23 on valve member16 causing spring 22 to b'ecompressed and consequent movement of thevalve assemblyto'the left against the opposing force of pressure stillacting on operating piston 18, so that throttle piston 25 is engaged andcarried along therewith by shoulder projection 31, while spring 30 isalso compressed. The relative pressure areas of pistons 18 and 20 andthe relative compressive ratings of spring 22 and 30 are such that valveassembly 14 is moved leftwardly only to an extent sufficient for closingoff vent valve 16 and moving throttle piston 25 to a throttling positionin which throttle area 26 is partially open to provide a throttlingaction on the resumed fluid pressure flow to braking cylinder 3. Thusthe braking pressure P present in the braking cylinder 3 is still activewhile the wheel continues to run. As a result, the braking pressure ismore efficiently utilized by the wheel during the period of reducedbraking pressure restoration thereof.

After the angular speed of the wheel has approximated the linear speedof the vehicle commensurate with the aforementioned specified rotaryacceleration of the wheel, detector device 34, in response to suchspecified rate of acceleration, operates to a first deenergizingposition for causing the energizing circuit 35 of magnet valve 19 to beopened again, so that magnet valve 19 resumes a venting position whicheffects closing of valve 37 and consequent (at time point t relief ofpressure acting on piston 18 via a vent 41 in said magnet valve device.Compressed spring 20 thus becomes effective to move the valve assembly14 further to the left until throttle piston 25 is restored to its openposition, in which throttle area 26 is fully reopened, and unrestrictedflow of braking pressure to cylinder 3, as initially established by theoperators brake valve device 7, is restored. Subsequently, detectordevice 34 is operated to a second deenergizing position in which circuit36 is reopened and magnet valve 24 is switched to a venting position inwhich valve 39 is closed and pressure acting on piston 20 is releasedvia a vent 42 in the magnet valve device. Due to the somewhat delayedoperation of magnet valve 24 to its venting position compared tooperation of magnet valve 19 to its vent ing position, a rapid leftwardmovement of valve assembly 14 to its nonnal position is positivelyeffected by the higher spring force of compressed spring 20. Throttlearea 26 is partially opened to provide throttling action when throttlepiston 25 is engaged by shoulder projection 31 and moved to the left,along with leftward movement of valve assembly 14, to a throttlingposition in which air tank 2 is connected to brake cylinder 3 throughthe partially closed or restricted throttle area. As a result of suchthrottling action, throttle piston 25 is subjected on the front orsupply side thereof to the full pressure from tank 2, whereas the backor delivery side of said piston subject to'the pressure as reduced'bythe throttling action, so that a resultant or differential force of suchpressures is established and directed in opposition to the force ofreturn spring 30.

Return spring 30 is so designed that the force of the pressuredifferential between the two sides of throttle piston 25 is initiallysufficient to overcome the force of the return spring 30 and to therebyhold throttle'piston 25 in the throttling position. Restoration ofbraking pressure in brake cylinder 3, therefore, is retarded accordingto the effective throttling action as throttle area 26. As a result, thebraking force is utilized more efficiently by the wheel duringrestoration of braking pressure. But if the braking pressure in thebrake cylinder 3 reaches a value lying somewhat below the maximumbraking pressure P (time point t,), then the force of the differentialpressure (which is thus reduced by equalizing action between the twosides of piston 25) is overcome by the force of spring 30, and thethrottle piston 25 is moved back by spring 30 into a non-throttlingposition in which throttle area 26 is fully open again and brakingpressure in the brake cylinder 3may rapidly build up again. As a result,the braking force is also utilized more efficiently by the wheel at theend of the restoration phase of the braking pressure.

The braking pressure P can easily be adjusted by replacing spring 30.with one having the desired compression rating and effect.

The anti-skid mechanism shown in FIG. 3 differs from the anti-skidapparatus shown in FIG. 1- in that the braking pressure control valvedevice is somewhat modified.

The anti-skid, apparatus shown in FIG. 3, similarly to that, shown in.FIG. 1, also includes a source of flfuidunder pressure or compressed airtank 102' communicable. with. a. braking cylinder 103 via pipes 104,105, and 106. Anoperators brake valvedevice 107, similar to brake valvedevice 7 describedrin connection with FIG. 1, is interposedbetweenpipes-104 and 105 for effectingsupply of fluidpressure fromtank 102 tobraking cylinder 103.

A braking pressure control valve-device 140-is interposed. between pipes105 and 106 and. comprises avalve housing 141, and a valve assembly142-including an operating piston143 of the diaphragm type, whichcooperates with a valve seat l44ato controlventingof upper end portionof piston stem 146 extends coaxially,

throughthrottle piston 148-andis movable relative thereto. The upperportion of bore 149 .is formed by aplurality of circularly arranged,angularlyspaced, radial fins 150which. cooperate with reduced portion136 of throttle piston 148 to provide a throttlearealsl controllable byreciprocable movement of said throttle pistonwithin the bore. Throttlearea 151is completely cutoff when reduced portion-1364s disposed=wholly. within the closed portion of bore 149.& Aretum spring.

152 is compressedly disposed between guidewall 147 i and the lower sideof throttle piston l48-.--.The;relativemovement between throttlepiston148-andpistonstem 146,.is' limited by a shoulder 153 formed at; theupper substantially intermediate the ends ofsaid piston stem, saidshoulders serving as stops for the throttle piston 148. Operating piston143 is subjectable to fluid pressure by operation of magnet valve device155. which is actuated when a conventional wheel-slip detector device156 causes an energizing circuit 157 to close or open in response toattainment of a certain wheel deceleration or acceleration values by thewheel.

According to the operation of the anti-skid device shown in FIG. 3, whenthe brakes are in'a released state, the several parts of the ariti-skidmechanism are in the respective positions in which they are shown insaid FIG. 3. In the brake released disposition of the apparatus,throttle area 151 is fully open and diaphragm piston 143, in the absenceof air pressure on the upper side thereof and with ,air pressure on thelower side thereof (via magnet valve 155), along with upwardly directedforce of spring 152 acting thereon through throttle piston 148 andvalvestem 146, occupies a supply position in which it is seated on valve seat144. Consequently, a venting communication between braking cylinder 3and an atmospheric port 158 formed in housing 141 isclosed. The throttlepiston 148 thus assumes an open or non-throttling position in which, asabove noted, throttle area 151 is fully open.

If a brake application is initiated by actuation of the operators brakevalve 107, and if the wheel deceleration should, as a result thereof,attain a skid threshold value, that is, exceed a value leading to theskidding of the wheel, the detector device 156 responds thereto foreffecting energization of magnet valve 155 and consequent release of airpressure on the lower side of piston 143, whereupon supply fluidpressure acting concurrently on the upper side thereof is effective formoving saidpiston downwardly to an unseated or venting position relativeto valve seat 144 and thereby initiates release of air pressure frombraking cylinder 3 via port 158; When operating piston 143 is thus moveddown wardly, throttle piston 148 is carried along with it by means ofshoulder 153', while return spring 152 is being compressed, to a closedor cut-ofi position in which throttle area. 151 is completely closedwhile braking pressure in the brake cylinder 103 continues to dc creaseuntil the deceleration rate of the wheel recovers to a value below theskid threshold; Detector device 156 responds to such decelerationrecovery of the wheel and causes magnetvalve 155 to be deenergized andcircuit 135 opened; so that air pressure is restored end of said pistonstem anda shoulder 154 disposed on the lower side of piston 143 whichis, therefore, moved to its seated position on valve seat 144 toterminate further'venting of braking pressure from cylinder 103; Aspiston 143 continues to move upwardly, valve stem 146 is carried alongtherewith until shoulder 154 engages throttle piston 148 and moves itinto a throttling position in which tank 102 is again connected to thebrake cylinder 103 through throttle area 151 to resume supply offluidpressure to said brake cylinder, but at a throttled rate according todegree to which said throttle area is opened. The throttle piston 148 isheld in the established throttling position until it is automaticallymoved back'to its open or non-throttling position atthe end of completerestoration of the braking pres sure-inbraking cylinder 103, as alreadydescribed for thevariantshowninFIG. 1.

The anti-skid mechanism according to FIG. 4 shows a further modificationof the braking pressure control valve device and the throttle mechanismincluded therein.

Similarly to the apparatus shown in FIGS. 1 and 3, the apparatus shownin FIG. 4 also includes a source of fluid under pressure or compressedair tank 202 communicable with a braking cylinder 203 via pipes 204,205, and 206. An operators brake valve device 207, also similar tooperators brake valve device 7 shown in FIG. 1, is interposed betweenpipes 204 and 205 for effecting supply of air pressure from tank 202 tobraking cylinder 203. A braking pressure control valve device 260 isinterposed between pipes 205 and 206 and comprises a housing 261 havingoperably disposed therein a throttle assembly 257 comprising a throttlepiston 262 having an axial bore 263 extending coaxially therethrough.Upward movement of throttle piston 262, as viewed in FIG. 4, is urged bya spring 264, such upward movement being limited by engagement of ashoulder formed on the piston with a stop ring fixed in housing 261. Thebraking pressure control valve device 260 also comprises a firstdiaphragm type operating piston 265 which, in cooperation with a valveseat 266 surrounding the upper end of bore 263 in throttle piston 262forms a fluid pressure admission valve, and a second diaphragm typeoperating piston 268 which, in cooperation with a valve seat 269surrounding one end of a passageway 270 formed in housing 261 andconnecting with pipe 206, forms a vent valve by which venting of fluidpressure from braking cylinder 203 via a vent port 267 is controlled.

The lower end of bore 263 in throttle piston 262 cooperates with acompatibly disposed housing shoulder 272 formed in housing 261 toprovide a throttle area 271 and, therefore, throttling action for fluidpressure supplied to braking cylinder 3. A supply chamber 273 disposedadjacent the lower side of diaphragm piston 265 isconnected to pipe 205.Operating pistons 265 and 268 are each actuable by magnet valve devices274 and 275, respectively. Magnetic valve devices 274 and 275 areenergizable by a conventional wheel-slip detector device 276, whichcloses or opens respective circuits 277 and 278 of the magnet valveswhen certain wheel deceleration or acceleration values are attained bythe wheel.

In operation of the anti-skid apparatus shown in FIG. 4, when the brakesare in a released state, the several parts of the anti-skid mechanismare in the respective portions in which they are shown and in whichdiaphragm piston 265 is in an unseated position relative to valve seat266, while diaphragm piston 268, due to the force of fluid pressureacting on the lower side thereof (via magnet valve 275) is in a seatedposition relative to valve seat 269. With throttle piston 262 in itsfully unseated position, there is no throttling action at throttle area271 between the lower end of said piston and shoulder 272. If a brakeapplication is initiated by actuation of the operators brake valve 207,the wheel deceleration attains a skid threshold, that is, exceeds thevalue leading to skidding of the wheel, the detector device 276, inresponse thereto, causes operation of magnet valve device 274 to admitfluid pressure on the upper side of piston 265 and operation of magnetvalve device 275 to release fluid pressure from the under or lower sideof piston 268. Consequently, piston 265 is moved downwardly to a seatedposition on valve seat 266, as a result of which supply of fluidpressure to brake cylinder 203 is terminated and throttle piston 262 isbrought into a throttling position while compressing the return spring264. Diaphragm piston 268,

as above noted, is simultaneously relieved of fluid pressure acting onthe lower side thereof and, as aresult of the braking pressure acting onthe upper side thereof, is moved downwardly to an unseated positionrelative to valve seat 269 resulting in release of braking pressure frombrake cylinder 203, until the rotary deceleration of the wheel fallsbelow thevalue leading to skidding. 1

When wheel deceleration value falls belowthe value leading to skidding,the detector 276 again responds to cause magnet valve devices 274 and275 to be switched back to their initial position whereby piston 265 isoperated to its unseated position again and piston 268 to its seatedposition. The throttle piston 262, now in its throttling position, issubjected on the upper or supply side to pressure in chamber 273 and onthe lower or delivery side to pressure prevailing in braking cylinder 3,thus establishing a pressure differential therebetween, the resultingforce of which is opposingly directed against the force of the returnspring 264. Thus, throttle piston 262 is held in its throttlingposition, so that restoration of braking pressure in the brake cylinder203 is delayed according to the throttling action established. Thethrottle piston is automatically restored to its non-throttling positionupon termination of restoration of braking pressure, as alreadydescribed for the embodiment according to FIG. 1.

The anti-skid apparatus shown in FIG. 5 differs from the anti-skidapparatus shown in FIG. 1 in that throttle means included thereincomprises a device separate from the braking or pressure control valvedevice.

The anti-skid apparatus shown in FIG. 5 also comprises a fluid pressureor compressed air tank 302 communicable with a braking cylinder 303 viapipes 304, 305, and 306. An operators brake valve device 307, alsosimilar to the operators brake valve 7 shown in FIG. 1, is interposedbetween pipes 304 and 305 for effecting supply of air pressure from tank302 to braking cylinder 303.

A solenoid-operated braking pressure control valve device 350 isconnected serially with a throttle valve device 351 by a pipe 352, saidcontrol valve device, throttle valve device, and pipe .352 all beinginterposed in serial relation to each other between pipes 305 and 306.The braking pressure control valve device 350 includes a piston (notshown) actuated by pressure medium under the control of a solenoid 353.The throttle valve device 351 comprises a valve housing 354 and athrottle piston 355 serving as a movable throttle member, which issealin'gly reciprocably operable within a sleeve 356 coaxially fixedadjacent the left-hand end of said housing, as viewed in FIG. 5. A valvestem 358 is axially operable within a guide sleeve 360 formed coaxiallywithin housing 354 substantially intermediate the ends thereof. Theleft-hand end of stem 358 rests against the adjacent inner face ofthrottle piston 355 with the other end thereof rigidly fixed to anoperating piston 362 which is capable of movement against the opposingforce of a return spring 361 compressed between said operating pistonand the right-hand end wall of housing 354. Movement of piston 362 islimited in a leftwardly direction by abutment of said piston against theadjacent end of guide sleeve 360 and in a rightwardly direction byabutment with the inner end of an adjustable stop screw 363 extendinginwardly and coaxially into housing 354 through the right-hand end wallof said housing.

Sleeve 356 is provided with an internal shoulder 364 serving as a stopfor leftward movement of throttle piston 355 and is also provided withaxially spaced pluralities of radial openings 365 and 366. Pipe 305 isconnected to an annular supply chamber 367 surrounding sleeve 356 inhousing 354 and thence via openings 365 to a spring chamber 368, inwhich a spring 369 is disposed for urging throttle piston 355 in arightwardly direction. Pipe 305 is also communicable with pipe 352 viasupply chamber 367 and openings 366. A control chamber 370 is formed inhousing 354 between an inner separating wall 371 and the left-hand sideof piston 362, and is chargeable with and relieved of operating pressureby a magnet valve 357 connected to tank 302 via a pipe 372.

Solenoid valve 353 and magnet valve 357 are energizable anddeenergizable by a conventional wheel-slip detector device 359, whichcloses or opens respective circuits 373 and 374 when certain wheeldeceleration or acceleration values are attained by the wheel,

In operation of the anti-skid apparatus shown in FIG. 5, when the brakesare in a released state, the, several parts thereof are in therespective positions shown in which fluid pressure is completely ventedfrom control chamber 370 and throttle piston 355 is urged by spring 361,through piston 362 and stem 358, against stop 364 while compressingspring 369. Pipe 305 is connected to brake cylinder 303 via chamber 367,openings 366, pipe 352, braking pressure control valve device 350, andpipe 306. If a brake application is initiated by actuation of theoperators brake valve device 307, the throttle piston 355 is subjectedon both sides, via chamber 367 and openings 365 and 366, with the samepressure from tank 302 and is. thereby held in an open or non-throttlingpositionin which it is shown, while braking pressure may build upunrestrictedly in brake cylinder 303.

If the wheel deceleration at this time exceeds a value leading to theskidding of the wheel, detector device 359 responds to such condition ofdeceleration to cause, in the usual manner, actuation of solenoid andmagnet valve devices 353 and 357, respectively. Braking pressure controlvalve 350 is shifted from a supply position, indicated S in the drawing,in which air pressure maybe supplied to brake cylinder 303, to a ventposition, indicated V in the drawing, for interrupting the connectionbetween the pipes 352 and 306, and venting pressure from said brakecylinder. Simultaneously, magnet valve device 357 causes air pressure tobe admitted into chamber 370, which results in effecting rightwardmovement of piston 362 and consequent compression of spring 361 untilsaid piston comes to rest against the inner end of stop screw 363. Sincestem 358 moves to the right along with piston 362, spring 369 iseffective in moving throttle piston 355 to the right until it assumes athrottling position in which openings 366 are partiallyblocked by saidpiston, so that pipes 305 and 352 are now connected through a throttlearea 375 formed cooperatively by the throttle piston 355 and openings366 in sleeve 356.

After the wheel, as a result of braking pressure reduction, obtains theapproximate linear speed of the vehicle, if the acceleration of thewheel again exceeds a certain value, detector device 369 responds againto. cause solenoid valve 353 and magnet valve 357 to be operated totheir respective initial positions. Braking pressure control valve 350is operated to position S,

thereby reestablishing connection between pipes 352 and 306, and airpressure in chamber 370' is again vented by operation of magnet valvedevice 357, so that the force of spring 361 again becomes active onthrottle piston 355 vianpiston 362 and stem 358. Throttle piston 355remains in the throttlingposition', however, because the combined forcesof spring 368 and the resultant forceof pressure differential caused bypressures on front and back sides of the throttle piston 355 aresufficient for overcoming the force of compressed spring 361 untilbraking pressure in brake cylinder 303 has been restored to the pointwhere such pressure differential is sufi'iciently neutralized to renderthe force ofspring 361 effective for overcoming the said combinedforcesand moving throttle piston 355 back into the non-throttling position.

The anti-skid apparatus shown in FIG. 6 differs from the anti-skidapparatus shown in FIG. 1 essentially in that the throttle means can beswitched pneumatically into the throttling position by the brakingpressure control valve simultaneously with initiation of brakingpressure reduction.

The anti-skid: apparatus shown in FIG. 6 also comprises a source offluid under pressure or compressed air tank 402 communicable with abraking cylinder 403 via pipes 404, 405, and 406. An operators brakevalve device 407, also similar to the operator's brake valve device 7shown in FIG. 1, is interposed between pipes 404 and 405 for effectingsupply of air pressure from tank 402 to braking cylinder 403.

In addition to a symbolically illustrated braking pressure control valvedevice 450 of the solenoid-operated type, the anti-skid apparatus alsocomprises a throttle valve device 451 which is interposed between pipe406, via which it is connected to braking cylinder 403, and a pipe 452,via which it is connected to said throttle valve device. Throttle valvedevice 451 is also connected to pipe 406 via a pipe 452 in bypassingrelation to control valve device 450. The braking pressure control valvedevice 450 includes pressure operable piston means (not shown) which isoperable under the control of a solenoid 454.

The throttle valve device 451 comprises a housing 455 and a movablethrottle piston 456 biased in a leftwardly direction, as viewed in thedrawing, by a return spring 457 and guided in said housing by aplurality of angularly spaced radial ribs 458 formed on theperipherythereof. The left-hand end of throttle member 456 forms a throttle plateor piston 459 which, in cooperation with an annular shoulder 460, formedcoaxially in housing 455, provides the throttling action, said shoulderserving also as the guide member in which ribs 458 are slidablydisposed. Throttle piston 456 is subjectable to fluid pressure on theleft or supply side thereof via pipe 405 and on the right or deliveryside thereof via pipe 453.

Solenoid 454 is actuable by means of a conventional wheel-slip detectordevice 462 which closes or opens an energizing circuit 463 for saidsolenoid when specified wheel deceleration or acceleration values,respectively, are attained by the wheel.

In operation of the anti-skid apparatus shown in FIG. 6, when the brakesare in a released state, the several partsof the anti-skid apparatus arein the respective positions shown in which throttle piston 456 is heldby return spring 457 in an open or non-throttling position, in which athrottle area 464 formed between the throttle plate 459 and shoulder 460is fully open, and pipeline 405 is connected to brake cylinder 403 viasaid throttle area, pipeline 452, braking pressure control valve device450, and pipeline 406. In the brakerelease disposition of the apparatus,control valve 450 occupies a supply position, indicated S in thedrawing, in which pipe 452 is in communication with pipe 406.

If a brake application is initiated by actuation of the brake valve 407,throttle piston 456 is, at the onset, subject to the same degree offluid pressure from tank 402 on the left or supply side through pipe 405and on the right or delivery side through the fully open throttle area464, pipe 452, control valve 450, and pipe 453, so that said throttlepiston is retained in its non-throttling position by return spring 457,while the braking pressure builds up in the brake cylinder 403. If thewheel deceleration at this time exceeds a specified value whichindicates that the skid threshold has been reached, detector device 462responds thereto to close circuit 463 and effect energization ofsolenoid 454. As a consequence, the braking pressure control valve 450is switched from position S to a vent position, indicated V in FIG. 6,in which braking pressure in brake cylinder 403 is reduced via pipe 406while pipe 452 is cut off from pipe 406. The pressure in pipe 453 isalso released at this time via control valve 450, while the pressure inpipe 405 is maintained. The throttle piston 466 is thus relieved offluid pressure acting on the right side thereof and moved into athrottling position against the opposing force of spring 457 only, inwhich throttling position the throttle area between the throttle plate459 and shoulder 460 is reduced to produce a throttling effect. Thethrottling action of throttle plate 459 establishes a pressuredifferential between the opposite sides of said plate which initially issufficient for overcoming the opposing force of return spring 457 andretaining said throttle plate in the throttling position for a delayedperiod of time.

Since the remaining manner of operation of the antiskid apparatus shownin FIG. 6, and especially of the throttle valve device 451 is similar tothe already described manner of operation of the embodiment shown inFIG. 1 and should be evident to one skilled in the art, furtherdescription of such remaining operation is not deemed essential to anunderstanding of the invention. The anti-skid apparatus, according tothe invention, is also characterized by simplicity of construction.Moreover, the invention provides the further advantage, when the brakesare released via braking valve 407, of immediately causing the throttlemeans to be switched to its non-throttling position due to the drop inthe braking pressure, so that no brake releasing difficulties can occur.

We claim: I

l. Anti-skid apparatus for a vehicle wheel comprising:

a. brake applying means operable responsively to fluid pressure forapplying a braking force to the wheel commensurate with the degree offluid pressure supplied thereto;

b. fluid pressure supply means including a source of fluid underpressure and an operators brake valve device selectively operable to aplurality of supply positions for effecting supply of fluid pressurefrom said source to said brake applying means at a measured pressuredetermined by the position to which the operators brake valve device isoperated for causing deceleration of the wheel at a rate normallycommensurate with said measured pressure;

c. braking pressure control means interposed between said brake,applying means and said fluid pressure supply means and having a normalposition in which unrestricted flow of fluid pressure supply to thebrake applying means, at said measured pressure, is effected, saidbraking pressure control means being operable tov a different positionin which interruption of braking pressure supply to the brake applyingmeans and reduction of such braking pressure therefromto atmosphere iseffected; and

d. wheel slip detector means operable responsively to wheel decelerationat a certain rate, at which the skid threshold of the wheel is reached,to a first dis position for eflecting operation of said braking pressurecontrol means to its said different position, and being operableresponsively to restoration of wheel deceleration to a rate compatiblewith that of linear deceleration of the vehicle to a second dispositionfor effecting restoration of said braking pressure control means to itssaid normal position;

wherein the improvement comprises:

e. a throttle piston disposed in said braking pressure control means inthe flow path of fluid pressure supplied to the brake applying means,said throttle piston having an open position in which said unrestrictedflow of pressure supply is effected and being operable, by initialmovement of the braking pressure control means from its said differentposition toward its said normal position, to a throttling position inwhich said reduction of braking pressure from the brake applying meansis terminated, and restoration of the braking pressure control means toits said normal position and, consequently, restoration of brakingpressure to said measured pressure is delayed according to apredetermined rate.

2. Anti-skid apparatus, as set forth in claim 1, wherein said throttlepiston assumes a cut-off position in the said different position of thebraking pressure control means for effecting said interruption ofbraking pressure supply to the brake applying means.

3. Anti-skid apparatus for a vehicle wheel, as set forth in claim 1,wherein said wheel slip detector means is also operable, subsequently tooperation of said braking pressure control means to its said differentposition and responsively to consequent restoration of wheel rotation toa rate below that corresponding to the wheel skid threshold, to a thirddisposition for effecting operation of the braking pressure controlmeans and said throttle piston to the throttling position.

4. Anti-skid apparatus, as set forth in claim 3, wherein the brakingpressure control means comprises:

a. differential piston means; and

b. valve means operable responsively to operation of said wheel slipdetector means to its said first, second, and third dispositions tocause operation of said differential piston means for effectingoperation of the braking pressure control means to said different,normal, and throttling positions, respectively.

5. Anti-skid apparatus, as set forth in claim 4,

wherein the wheel slip detector means comprises an electrical wheel slipdetector device and said valve means comprises electrically operablemagnet valve means. I

6. Anti-skid apparatus, as set forth in claim 3, wherein said brakingpressure control means comprises a valve assembly including:

a. a valve stem;

b. a first operating piston fixed at one end of said valve stem andsubjectable to fluid pressure from said source by operation of saidwheel slip detector means to its said first disposition for operatingthe braking pressure control means to its said different position; i

c. a second operating piston having a larger pressure area than saidfirst operating piston and carried at the opposite end of said valvestem in operably opposing relation to said first operating piston andwith limited axial movement relative to the valve stem, said secondoperating piston being subjectable to fluid pressure from said source,by operation of said wheel slip detector means to its said thirddisposition, and being operable responsively to said fluid pressure forovercoming opposing fluid pressure acting on said first operating pistonand effecting operation of the valve assembly and said throttle pistonto said throttling position; and

d. a vent valve member fixed on said valve stem in such an axialposition as to occupy a closed position, in which communication betweensaid brake applying means and atmosphere is cut off, in both the normaland throttling positions of thebraking pressure control means, and anopen position in which said communication is open in the differentposition of the braking pressure control' means;

e. said throttle piston being carried on said valve stem adjacent saidfirst operating piston 'andhaving limited axial movement relative to thevalve stem for effecting said interruption and for throttling saidsupply of fluid pressure to the brake applying means in the difierentposition and the throttling position, respectively, of the brakingpressure control means.

7. Anti-skid apparatus, as set forth in claim 6, wherein'said first andsecond operating pistons'are of the diaphragm type.

8. Anti-skid apparatus, as set forth in.claim 6, wherein said valveassembly further comprises:

a. first biasing means acting on said first operating piston throughsaid throttle piston in opposition to the fluid pressure acting on saidfirst operating piston; and

b. second biasing means acting on said second operating piston inopposition to the fluid pressure acting thereon, said first and secondbiasing means being of such calibration and acting cooperatively withthe opposing fluid pressures acting on the respective operating pistonsas to maintain said valve assembly and the throttle piston in saidthrottling position until said measured pressure has been restored inthe brake applying means and the braking pressure control means has beenrestored to its said normal position. '9. Anti-skid apparatus, as setforth in claim 2, wherein said braking pressure control'means comprises:

a. a valve'stem having said throttle piston mounted at one end thereofwith limited axial movement relative thereto;

lb. compressible biasing means for urgingsaid throttle piston to an openposition against said one end of the valve stem and in which saidunrestricted flow of fluid pressure supplyv to the brake applying meansis effected; and I c. a diaphragm type operating piston fixed to theopposite end of said valve stem, normally subjectable to equal fluidpressures on opposite sides thereof, and being operable by saidbiasing-means, acting through said throttle piston and said valve stem,to a supply positionfor effecting operation of the braking pressurecontrol means to its said normal position, said operating piston beingoperable, responsively to reduction of fluid pressure from one sidethereof by said wheel slip detector means in its said first disposition,to a .venting position for effecting operation of the braking pressurecontrol means to its said different position in which said throttlepiston initially assumes its said throttling position,

d. said throttle piston, in said throttling position, being subject to apressure differential established thereacross by fluid at said measuredpressure acting on one side thereof and pressure prevailing in saidbrake applying means acting on the opposite side thereof, subsequentlyto operation of the braking pressure control means to its said differentposition, said pressure differential being effective for maintainingsaid throttle piston in its said throttling position until pressureacting on the opposite side thereof has been restored to said measuredpressure.

10. Anti-skid apparatus, as set forth in claim 2',

wherein said braking pressure control means comprises:

a. a control valve device including biasing means for operating saidcontrol valve device to a supply position, in which fluid pressuresupply to the brake applying means is effected, and being operable,responsively to operation of said wheel slip detector means to its saidfirst disposition, to a venting position in which said interruption ofbraking pressure supply to and reduction thereof from the brake applyingmeans is effected;

an operating piston fixed at one end of a valve stem and having one sidethereof subjectable to fluid pressure by operation of the wheel slipdetector means to its said first disposition and relieved of suchpressure in the second disposition of said wheel slip detector means,the other end of said consequent neutralization of the biasing efiect ofsaid first biasing means, for operating the throttle piston to its saidthrottling position,

e. said throttle piston being restorable to its said open position bysaid first biasing means and said control valve device being restorableto its said supply position responsively to operation of the wheel slipdetector means to its said second disposition.

ll. Anti-skid apparatus, as set forth in claim 2,

wherein said braking pressure control means comprises:

a. a control valve device normally occupying a supply position in whichsaid unrestricted flow of fluid pressure supply to the brake applyingmeans is effected, and being operable, responsively to operation of saidwheel slip detector means to its said first disposition, to a ventingposition in which said interruption of braking pressure to and reductionthereof from the brake applying means is efiected; and

b. biasing means acting on one side of said throttle piston for urgingthe throttle piston toward its said open position, said throttle pistonbeing subject on the opposite side to fluid at said measured pressure 16and on said one side to the fluid pressure prevailing in the brakeapplying means,

. said throttle piston being operable to its said throttling positionresponsively to reduction of fluid pressure acting on said one side aseffected by operation of said control-valve device to its said ventingposition and being subject, in said throttling position, to a pressuredifferential thereacross established by the respective fluid'pre'ssuresacting on the opposite sides of the throttlepiston, said pressuredifferential being effective for delaying restoration of brakingpressure in the brake applying means to said measured pressure for apredetermined period subsequently to restoration of said control valvedevice to its said supply position. k =0

1. Anti-skid apparatus for a vehicle wheel comprising: a. brake applyingmeans operable responsively to fluid pressure for applying a brakingforce to the wheel commensurate with the degree of fluid pressuresupplied thereto; b. fluid pressure supply means including a source offluid under pressure and an operator''s brake valve device selectivelyoperable to a plurality of supply positions for effecting supply offluid pressure from said source to said brake applying means at ameasured pressure determined by the position to which the operator''sbrake valve device is operated for causing deceleration of the wheel ata rate normally commensurate with said measured pressure; c. brakingpressure control means interposed between said brake applying means andsaid fluid pressure supply means and having a normal position in whichunrestricted flow of fluid pressure supply to the brake applying means,at said measured pressure, is effected, said braking pressure controlmeans being operable to a different position in which interruption ofbraking pressure supply to the brake applying means and reduction ofsuch braking pressure therefrom to atmosphere is effected; and d. wheelslip detector means operable responsively to wheel deceleration at acertain rate, at which the skid threshold of the wheel is reached, to afirst disposition for effecting operation of said braking pressurecontrol means to its said different position, and being operableresponsively to restoration of wheel deceleration to a rate compatiblewith that of linear deceleration of the vehicle to a second dispositionfor effecting restoration of said braking pressure control means to itssaid normal position; wherein the improvement comprises: e. a throttlepiston disposed in said braking pressure control means in the flow pathof fluid pressure supplied to the brake applying means, said throttlepiston having an open position in which said unrestricted flow ofpressure supply is effected and being operable, by initial movement ofthe braking pressure control means from its said different positiontoward its said normal position, to a throttling position in which saidreduction of braking pressure from the brake applying means isterminated, and restoration of the braking pressure control means to itssaid normal position and, consequently, restoration of braking pressureto said measured pressure is delayed according to a predetermined rate.2. Anti-skid apparatus, as set forth in claim 1, wherein said throttlepiston assumes a cut-off position in the said different position of thebraking pressure control means for effecting said interruption ofbraking pressure supply to the brake applying means.
 3. Anti-skidapparatus for a vehicle wheel, as set forth in claim 1, wherein saidwheel slip detector means is also operable, subsequently to operation ofsaid braking pressure control means to its said different position andresponsively to consequent restoration of wheel rotation to a rate belowthat corresponding to the wheel skid threshold, to a third dispositionfor effecting operation of the braking pressure control means and saidthrottle piston to the throttling position.
 4. Anti-skid apparatus, asset forth in claim 3, wherein the braking pressure control meanscomprises: a. differential piston means; and b. valve means operableresponsively to operation of said wheel slip detector means to its saidfirst, second, and third dispositions to cause operation of saiddifferential piston means for effecting operation of the brakingpressure control means to said different, normal, and throttlingpositions, respectively.
 5. Anti-skid apparatus, as set forth in claim4, wherein the wheel slip detector means comprises an electrical wheelslip detector device and said valve means comprises electricallyoperable magnet valve means.
 6. Anti-skid apparatus, as set forth inclaim 3, wherein said braking pressure control means comprises a valveassembly including: a. a valve stem; b. a first operating piston fixedat one end of said valve stem and subjectable to fluid pressure fromsaid source by operation of said wheel slip detector means to its saidfirst disposition for operating the braking pressure control means toits said different position; c. a second operating piston having alarger pressure area than said first operating piston and carried at theopposite end of said valve stem in operably opposing relation to saidfirst operating piston and with limited axial movement relative to thevalve stem, said second operating piston being subjectable to fluidpressure from said source, by operation of said wheel slip detectormeans to its said third disposition, and being operable responsively tosaid fluid pressure for overcoming opposing fluid pressure acting onsaid first operating piston and effecting operation of the valveassembly and said throttle piston to said throttling position; and d. avent valve member fixed on said valve stem in sucH an axial position asto occupy a closed position, in which communication between said brakeapplying means and atmosphere is cut off, in both the normal andthrottling positions of the braking pressure control means, and an openposition in which said communication is open in the different positionof the braking pressure control means; e. said throttle piston beingcarried on said valve stem adjacent said first operating piston andhaving limited axial movement relative to the valve stem for effectingsaid interruption and for throttling said supply of fluid pressure tothe brake applying means in the different position and the throttlingposition, respectively, of the braking pressure control means. 7.Anti-skid apparatus, as set forth in claim 6, wherein said first andsecond operating pistons are of the diaphragm type.
 8. Anti-skidapparatus, as set forth in claim 6, wherein said valve assembly furthercomprises: a. first biasing means acting on said first operating pistonthrough said throttle piston in opposition to the fluid pressure actingon said first operating piston; and b. second biasing means acting onsaid second operating piston in opposition to the fluid pressure actingthereon, said first and second biasing means being of such calibrationand acting cooperatively with the opposing fluid pressures acting on therespective operating pistons as to maintain said valve assembly and thethrottle piston in said throttling position until said measured pressurehas been restored in the brake applying means and the braking pressurecontrol means has been restored to its said normal position. 9.Anti-skid apparatus, as set forth in claim 2, wherein said brakingpressure control means comprises: a. a valve stem having said throttlepiston mounted at one end thereof with limited axial movement relativethereto; b. compressible biasing means for urging said throttle pistonto an open position against said one end of the valve stem and in whichsaid unrestricted flow of fluid pressure supply to the brake applyingmeans is effected; and c. a diaphragm type operating piston fixed to theopposite end of said valve stem, normally subjectable to equal fluidpressures on opposite sides thereof, and being operable by said biasingmeans, acting through said throttle piston and said valve stem, to asupply position for effecting operation of the braking pressure controlmeans to its said normal position, said operating piston being operable,responsively to reduction of fluid pressure from one side thereof bysaid wheel slip detector means in its said first disposition, to aventing position for effecting operation of the braking pressure controlmeans to its said different position in which said throttle pistoninitially assumes its said throttling position, d. said throttle piston,in said throttling position, being subject to a pressure differentialestablished thereacross by fluid at said measured pressure acting on oneside thereof and pressure prevailing in said brake applying means actingon the opposite side thereof, subsequently to operation of the brakingpressure control means to its said different position, said pressuredifferential being effective for maintaining said throttle piston in itssaid throttling position until pressure acting on the opposite sidethereof has been restored to said measured pressure.
 10. Anti-skidapparatus, as set forth in claim 2, wherein said braking pressurecontrol means comprises: a. a control valve device including biasingmeans for operating said control valve device to a supply position, inwhich fluid pressure supply to the brake applying means is effected, andbeing operable, responsively to operation of said wheel slip detectormeans to its said first disposition, to a venting position in which saidinterruption of braking pressure supply to and reduction thereof fromthe brake applying means is effected; an operating piston fixed at oneend of a valve stem and having one side thereof subjectable to fluidpressure by operation of the wheel slip detector means to its said firstdisposition and relieved of such pressure in the second disposition ofsaid wheel slip detector means, the other end of said valve stem makingabutting contact with one side of said throttle piston; first biasingmeans acting on the opposite side of said operating piston for biasingsaid throttle piston, through the operating piston and the valve stem,to its said open position; and d. second biasing means acting on theopposite side of said throttle piston and effective upon pressurizationof said one side of the operating piston and consequent neutralizationof the biasing effect of said first biasing means, for operating thethrottle piston to its said throttling position, e. said throttle pistonbeing restorable to its said open position by said first biasing meansand said control valve device being restorable to its said supplyposition responsively to operation of the wheel slip detector means toits said second disposition.
 11. Anti-skid apparatus, as set forth inclaim 2, wherein said braking pressure control means comprises: a. acontrol valve device normally occupying a supply position in which saidunrestricted flow of fluid pressure supply to the brake applying meansis effected, and being operable, responsively to operation of said wheelslip detector means to its said first disposition, to a venting positionin which said interruption of braking pressure to and reduction thereoffrom the brake applying means is effected; and b. biasing means actingon one side of said throttle piston for urging the throttle pistontoward its said open position, said throttle piston being subject on theopposite side to fluid at said measured pressure and on said one side tothe fluid pressure prevailing in the brake applying means, c. saidthrottle piston being operable to its said throttling positionresponsively to reduction of fluid pressure acting on said one side aseffected by operation of said control valve device to its said ventingposition and being subject, in said throttling position, to a pressuredifferential thereacross established by the respective fluid pressuresacting on the opposite sides of the throttle piston, said pressuredifferential being effective for delaying restoration of brakingpressure in the brake applying means to said measured pressure for apredetermined period subsequently to restoration of said control valvedevice to its said supply position.